1. Field of the Invention
The present invention relates to a laser processing apparatus capable of retracting a processing nozzle when electric power supply to a laser processing unit is cut off due to a power outage, etc.
2. Description of the Related Art
Generally, in laser processing, a distance between a nozzle and a workpiece is detected by a gap sensor, and the workpiece is processed by performing a gap control based on the detected value of the gap sensor. Thus, if an abnormality occurs in supply power due to a power outage, etc., the gap sensor may malfunction, and the gap control may be performed based on an erroneously detected value from the gap sensor, which may cause the processing nozzle to hit the workpiece.
It is known to provide an apparatus wherein provisions are made to prevent a processing head from dropping and hitting the workpiece when power supply to a laser processing unit is cut off due to a power outage, etc. For example, Japanese Examined Utility Model Publication No. H03-44388 (JP H03-044388 Y) discloses an apparatus in which a hydraulic cylinder is provided in the lower part of a ball screw for vertically moving a processing nozzle, and an engaging member is shifted upward by spring force when hydraulic oil is evacuated from a cylinder chamber of the hydraulic cylinder in the event of a power outage. In this configuration, an engaging portion of the engaging member engages with a mating portion of a mating member in the lower part of the ball screw, so as to prevent the ball screw from rotating.
On the other hand, Japanese Patent No. 2751766 (JP 2751766 B) discloses an apparatus in which a stopper is provided to protrude from a movable part formed integrally with a processing head and another stopper for adjusting a processing position is provided below the protruding stopper. In this configuration, when the processing head drops in the event of a power outage, the stoppers are abutted to each other, and thereby prevent the processing head from hitting the workpiece.